Dry analysis materials and methods for quantitative analysis of aqueous fluid sample utilizing them are described in U.S. Pat. Nos. 2,846,808, 3,016,292, 3,036,893, 3,368,872 and 3,552,928.
Dry, multilayer analysis materials composed of a transparent support having thereon at least one reagent layer and a porous layer, in this order, and quantitative analysis methods of aqueous fluid samples using those materials are described, e.g., in U.S. Pat. Nos. 3,992,158, 3,983,005, 4,042,335, 4,066,403, 4,144,306, 4,132,528, 4,258,001, 4,357,363, 4,381,921 and 4,292,272 and Japanese Unexamined Patent Publication No. 24576/81, H.G. Curme et al. and R.W. Spayd et al., Clinical Chemistry, vol. 24, pp. 1,335-1,350 (1978), Bert Walter, Anal. Chem., vol. 55, No. 4, pp. 498.congruent.514 (1983) and so on. The feasibility of using not only diluted serum and blood plasma as a sample, but also non-diluted whole blood, is described.
More specifically, examples of clinical tests to determine blood-glucose concentrations within a short time by using non-diluted whole blood as a sample and a multilayer-film analytical element are described in Ohkubo et al, Clinical Chemistry, vol 27, pp. 1,287-1,290 (1981).
Such materials typically contain a porous spreading layer that filters out at least a good portion of the solid components of whole blood, allowing the fluid component to pass through to a color-forming reagent layer or layers.
It is required that the porous spreading layer permit a drop of aqueous fluid sample applied thereto first to spread rapidly in a circle in the horizontal direction and then, to penetrate in a vertical direction, supplying the aqueous fluid to the reagent layer located thereunder in an approximately constant volume per unit area. This function is called a spreading function or a metering function. Cotton or polyester fabrics and knits, membrane filter-form nonfibrous isotropic porous materials, porous materials made of bound granules, paper such as filter paper for chemical analysis, e.g., Toyo Roshi No. 2 made by Toyo Roshi Co., Ltd., and so on satisfy these requirements. In particular, employing textile fabrics, knits, or granular constructions of fine granules containing continuous pores described in U.S. Pat. Nos. 4,258,001, 4,357,363 and 4,381,921 permits the quantitative analysis of whole blood, because the materials possess a spreading function with respect to not only blood plasma and serum but also whole blood containing a solid component.
When the quantitative analysis of a particular analyte in sample solutions, especially whole blood, blood plasma, serum, urine and similar samples, is performed in clinics, periodic measurements are generally performed using a solution containing the analyte in a definite amount in order to determine the precision of the analysis system. The solution used is, in general, called a control solution or a standard solution. In addition, solutions containing the analyte in known amounts are used for preparing a calibration curve. These solutions are generally called calibrators of calibration solutions by those skilled in the art.
Although pooled blood obtained by mixing a number of whole-blood specimens, or pooled sera prepared by mixing serum samples are adopted as a control solution and calibration solutions in some cases, the composition varies with the lot. Further, pooled blood and serum are difficult to preserve. Therefore, calibration solutions are generally simple aqueous solutions containing given amounts of analyte alone, or additionally containing a hydrophilic polymer (e.g., polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene glycol, etc.), plasma protein, or the like. (The aqueous solutions containing plasma protein are, in general, prepared by re-dissolving the lyophilized solid matter in water at the time of use.)
When calibration solutions of this kind are applied to the quantitative analysis of a particular component in fluid with dry analysis elements, particularly whole-blood analyses with dry analysis elements, the required color-producing reaction does not take place uniformly in the reagent layer(s). Accordingly, the application of such calibration solutions has the disadvantage that within-run reproducibility (precision) in color density measurements is poor. Moreover, since there is a difference in response to the analyte content, e.g., in color formation, between such calibration solutions and whole-blood samples, a calibration curve based on such calibration solutions has the defect that it deviates from the true calibration curve of whole-blood samples.